Since Russia’s forceful takeover of Crimea in 2014, both Moscow and NATO have deployed troops and weapons along old lines as tensions have grown to their highest since the end of the Cold War.

Analysts warn the dangers of a military confrontation are growing.

Russia has deployed nuclear-capable Iskander missiles to its westernmost exclave of Kaliningrad, which borders NATO members Poland and Lithuania.

Moscow’s S-400 surface-to-air missile batteries have also been stationed along its western frontiers. The Kremlin has staged regular military exercises along its western flank.

In response, NATO has put 300,000 troops on high alert and made so-called tripwire deployments in frontline states.

Communication was largely severed following Russia’s invasion of Crimea – and that raises the prospect of an accidental escalation, warns NATO’s former information officer in Moscow, John Lough, now of the Chatham House research organization.

FILE - Troops without insignia, believed to be Russian soldiers, guard the center of Simferopol, Crimea, March 27, 2014.

“It seems to me that it is actually very important to have mechanisms in place that allow the military establishments to communicate when needed. Both sides should see that there is the capacity here for some sort of accident,” he said.

NATO is deploying an extra 4,000 multinational troops to the Baltic states and Poland in the coming months. The core NATO principle of collective defense is being revitalized, said Lough.

“NATO is starting if you like from a low base in terms of rebuilding this defensive capability. It’s not the sort of thing that happens overnight; but, I would argue that the evidence of political will here in fact is probably more important,” he said.

Donald Trump’s victory in the November U.S. election has triggered uncertainty over the future commitment of NATO’s primary force.

The U.S. spent $66 billion on defense in 2016; second-placed Britain spent less than a tenth of that figure. President-elect Trump has questioned the U.S. financial burden – and Russia analyst Sarah Lain of the Royal United Services Institute says Moscow is watching with interest.

“Collective defense has actually I think psychologically at least been a huge deterrent for Russia. Trump may change that calculation, if he certainly pledges not to come to NATO allies’ help in a situation of need if they haven’t paid their 2 percent defense spending,” said Lain.

President-elect Trump’s praise for Russian leader Vladimir Putin has rattled Ukraine, which is battling pro-Kremlin rebels in the east.

“That will allow or embolden Russia to maybe test the boundaries of NATO and test the unity of NATO even further,” she said.

John Lough argues it is premature to assume that Trump’s early overtures to Moscow will translate into improved relations that will last.

“There are going to be areas where they will disagree. The perception of Iran, for example, is one of them and I think that will come to the fore quickly,” he said.

Trump also faces divisions at home within his own Republican party. U.S. senators, including former presidential candidate John McCain, visited Estonia and Georgia recently to reassure them of U.S. support in the face of Russian aggression.

Analysts say the rapid rearmament on both sides has raised the stakes – and the new U.S. administration will likely herald yet more uncertainty in an increasingly tense environment.